The present invention relates to a component of quartz glass for use in semiconductor manufacture, which component at least in a near-surface region shows a co-doping of a first dopant and of a second dopant, the second dopant containing one or more rare-earth metal oxides in a concentration of 0.1-3% by wt. each (based on the total mass of SiO2 and dopant).
Furthermore, the present invention relates to a method for producing such a component of quartz glass for use in semiconductor manufacture according to any one of the preceding claims, the method comprising providing SiO2 raw material in particulate form, providing the SiO2 raw material with a second dopant comprising one or more rare-earth metal oxides in a concentration of 0.1-3% by wt. each (based on the total mass of SiO2 and dopant), and sintering or melting the SiO2 raw material provided with the second dopant to obtain a quartz glass blank.
Yield and electrical operative behavior of semiconductor devices essentially depend on the extent to which semiconductor fabrication succeeds in preventing contamination of the semiconductor material caused by impurities acting as “semiconductor poisons”. Contamination of the semiconductor material is e.g. caused by the apparatuses used in the fabrication process. On account of the chemical resistance of quartz glass to a great number of substances used in the fabrication process and on account of its relatively high thermal stability, apparatuses of such types often consist of quartz glass. Therefore, high demands are made on the purity of quartz glass. Therefore, the apparatuses are more and more provided with specifically cleaned or treated layers, or synthetically produced quartz glass is used that is distinguished by high purity.
A jig of the above-mentioned type is known from JP 10-114532 A. The document describes a so-called “single wafer jig” of synthetic quartz glass which is distinguished by a low content of the impurities Fe, Cu, Cr and Ni, each being less than 10 ppb, and by a hydroxyl group content in the range between 100 ppm and 1000 ppm.
In this respect the known quartz glass jig is well suited for use in semiconductor manufacturing processes. In plasma etch processes in which the semiconductor substrates (wafers) are subjected to gases and plasmas having an etching effect, e.g. CF4, CHF3, C2F6, C3F8, NF3 or SF6, a further problem is however that the quartz glass is slowly corroded due to the reaction between SiO2 and fluorine. SiO2 is removed in this process and the surface gets worn in the end or changed so much that the quartz glass jig must be replaced.
It is known that the dry etching resistance can be improved by doping the quartz glass, for instance, with oxides of rare-earth elements, such as Y, La, Ce, Nd, Sm, and Gd. A significant effect, however, requires a high concentration of said dopants, which may lead to precipitations, phase separation and crystallization.
To avoid such situations, US 2005/0272588 A1, which discloses a quartz glass component and a method according to the above-mentioned type, suggests a co-doping of rare-earth metal oxide as the second dopant with an element of group 3B of the periodic table as the first dopant, and here particularly aluminum oxide. A maximum concentration of 2% by wt. is indicated for each of the second dopants, and a total dopant concentration ranging from 0.1 to 20% by wt.
Moreover, this document suggests several procedures for producing a correspondingly doped quartz glass blank, wherein according to a preferred method SiO2 raw material in particulate form is mixed with powder-like oxides of the dopants and the mixture is sintered in a quartz glass tube under a negative pressure.
However, it has been found that although such a co-doping with aluminum oxide may achieve an improved solubility of the additional dopant (apart from aluminum oxide), and thereby increase the dry etching resistance of the quartz glass, at least some of said dopant combinations may entail unexpected drawbacks. For instance, a discoloration of the quartz glass that is not desired for some applications is observed in the combination of Al and Nd, and the combination of Al and Y may result in a specific particle formation during use of the quartz glass in a plasma etch process with fluorine-containing etching gas.